The catalyst solutions and the processes of the present invention are useful for the production of aldehydes, ketones, and carboxylic acids, which are chemicals of commerce and/or feedstocks for the production of chemicals and materials of commerce. For example, acetone, methyl ethyl ketone and methyl isobutyl ketone are used as solvents. Acetaldehyde is used in the production of acetic acid, polyols, and pyridines. Acetic acid is used in the production of vinyl acetate, cellulose acetate, and various alkyl acetate esters which are used as solvents. Acetone is used in the production of methylmethacrylate for polymethylmethacrylate. Cyclohexanone is used in the production of caprolactam for nylon-6 and adipic acid for nylon-6,6. Other cyclic ketones can be used for the production of other nylon-type polymers.
Acetaldehyde is industrially produced by the Wacker oxidation of ethylene by dioxygen, which uses an aqueous catalyst system of palladium chloride, copper chloride, and hydrochloric acid to accomplish the following net conversion: EQU C.sub.2 H.sub.4 +1/2O.sub.2 .fwdarw.CH.sub.3 CHO (1)
Reviews of the Wacker process chemistry and manufacturing processes for the direct oxidation of ethylene to acetaldehyde can be found in "The Oxidation of Olefins with Palladium Chloride Catalysts", Angew. Chem. internat. Edit., Vol. 1 (1962), pp. 80-88, and in Chapter 8 of Ethylene and its Industrial Derivatives, S. A. Miller ed., Ernest Benn Ltd., London, 1969, each of which is incorporated by reference entirely. Aspects of Wacker technology are also disclosed in U.S. Pat. Nos. 3,122,586, 3,119,875, and 3,154,586, each incorporated by reference entirely.
In the Wacker process chemistry, ethylene is oxidized by cupric chloride in aqueous solution, catalyzed by palladium: ##STR1##
In a typical manufacturing operation, copper is present in the aqueous solution at concentrations of about 1 mole per liter, total chloride is present at concentrations of about 2 moles per liter, and the palladium catalyst is present at concentrations of about 0.01 moles per liter. Under these conditions, palladium(II) exists predominantly as the tetrachloropalladate ion, PdCl.sub.4.sup.=. Cuprous chloride resulting from the oxidation of ethylene is solubilized in the aqueous solution by the co-produced hydrochloric acid, as the dichlorocuprate ion, Cu.sup.l Cl.sub.2.sup.-. In a subsequent Wacker chemistry step, this reduced copper is reoxidized by reaction with dioxygen: EQU 2Cu.sup.l Cl.sub.2.sup.- +2H.sup.+ +1/2O.sub.2 .fwdarw.2Cu.sup.ll Cl.sub.2 +H.sub.2 O (3)
(Reactions (2) and (3) combined give overall reaction (1))
Two acetaldehyde manufacturing processes, a two-stage process and a one-stage process, have been developed and operated using the Wacker system chemistry. In the two-stage process, ethylene oxidation by cupric chloride, reaction (2), and reoxidation of cuprous chloride by air, reaction (3), are conducted separately, with intermediate removal of the acetaldehyde product from the aqueous solution. The reoxidized aqueous solution is recycled to the ethylene oxidation stage. The reactions are conducted at temperatures of about 100 to 130.degree. C. in reactors which, by providing very efficient gas-liquid mixing, result in high rates of diffusion (mass transfer) of the reacting gas into the aqueous solution. Under these conditions, about 0.24 moles ethylene per liter of solution can be reacted within about 1 minute in the ethylene reactor, corresponding to an average ethylene reaction rate of about 4 (millimoles/liter)/second. With a typical palladium concentration of about 0.01 moles per liter, this corresponds to a palladium turnover frequency (a measure of catalyst activity) of about 0.4 (moles C.sub.2 H.sub.4 /mole Pd)/second. In the air reactor, about 0.12 moles dioxygen per liter of solution can be reacted within about 1 minute, corresponding to an average dioxygen reaction rate of about 2 (millimoles/liter)/second.
In the one-stage process, ethylene and dioxygen are simultaneously reacted with the aqueous solution, from which acetaldehyde is continuously removed.
Palladium catalyzes the oxidation of ethylene by cupric chloride (reaction (2)) by oxidizing ethylene (reaction (4)) and then reducing cupric chloride (reaction (5)): EQU C.sub.2 H.sub.4 +PdCl.sub.4.sup.= +H.sub.2 O.fwdarw.CH.sub.3 CHO+Pd.sup.0 +2H.sup.+ +4Cl.sup.- ( 4) EQU Pd.sup.0 +4Cl.sup.- +2Cu.sup.ll Cl.sub.2 .fwdarw.PdCl.sub.4.sup.= +2Cu.sup.l Cl.sub.2.sup.- ( 5)
Functionally, the copper chlorides mediate the indirect reoxidation of the reduced palladium(0) by dioxygen via reaction (5) plus reaction (3). Direct oxidation of palladium(0) by dioxygen is thermodynamically possible but is far too slow for practical application.
The overall rate of oxidation of ethylene by the Wacker system is limited by the rate of oxidation of ethylene by the tetrachloropalladate (reaction (4)). The reaction rate is inversely dependent on both the hydrogen ion concentration and the square of the chloride ion concentration, having the following concentration dependencies: EQU C.sub.2 H.sub.4 reaction rate.varies.[PdCl.sub.4.sup.= ][C.sub.2 H.sub.4 ]/[H.sup.+ ][Cl.sup.- ].sup.2 ( 6)
Two chloride ions must be dissociated from tetrachloropalladate before palladium(ll) productively binds both the substrates of reaction (4), ethylene and water. Said another way, chloride competes with the two substrates for the third and fourth coordination sites on palladium(ll). This occurs by the following equilibria: EQU PdCl.sub.4.sup.= +C.sub.2 H.sub.4 .revreaction.PdCl.sub.3 (C.sub.2 H.sub.4).sup.- +Cl.sup.- ( 7) EQU PdCl.sub.3 (C.sub.2 H.sub.4).sup.- +H.sub.2 O.revreaction.PdCl.sub.2 (C.sub.2 H.sub.4)(H.sub.2 O)+Cl.sup.- ( 8)
Not only does chloride ion competitively inhibit the binding of substrates, but the remaining bound chlorides in intermediate complexes diminish the electrophilicity (positive charge density) at the palladium(ll) center which drives the overall reaction to palladium(0). The subsequent reaction steps, hydrogen ion dissociation (reaction (9)) and collapse of the resulting intermediate to products (reaction (10)), are less favored for these chloride-bound intermediate complexes that they would be for their aquated counterparts with fewer or no bound chlorides. EQU PdCl.sub.2 (C.sub.2 H.sub.4)(H.sub.2 O).revreaction.PdCl.sub.2 (C.sub.2 H.sub.4)(OH).sup.- +H.sup.+ ( 9) EQU PdCl.sub.2 (C.sub.2 H.sub.4)(OH).sup.- .fwdarw.CH.sub.3 CHO+Pd.sup.0 +H.sup.+ +2Cl.sup.- ( 10)
A step in reaction (10) is turnover rate-limiting for reaction (4) in the Wacker system (reactions (7), (8), (9), and (10) give reaction (4)), so that the disfavoring influences of chloride ion on reaction (10) and on the preceding equilibria (7), (8), and (9) are manifested in the obtained palladium catalyst activity.
However, the Wacker system requires a high total chloride concentration to function effectively. The chloride to copper ratio must be greater than 1:1 for the copper(ll) to be soluble CuCl.sub.2 rather than insufficiently soluble copper hydroxide chlorides, and for copper(l) to be soluble CuCl.sub.2.sup.- rather than insoluble CuCl. Moreover, in the absence of chloride, aquated copper(ll) is thermodynamically impotent for oxidizing palladium(0) metal to aquated palladium(ll). Chloride complexation raises the copper(ll)/copper(l) oxidation potential and lowers the palladium(ll)/palladium(0) oxidation potential, so that at high chloride ion concentrations the forward reaction (5) becomes thermodynamically favored.
The Wacker system has several undesirable characteristics in the manufacture of acetaldehyde. These undesirable characteristics result from the high cupric chloride concentration. The aqueous cupric chloride solution is extremely corrosive; manufacturing process equipment is constructed of expensive corrosion resistant materials, usually titanium. The manufacturing processes typically convert a percent or more of the ethylene feed to chlorinated organic by-products. These chlorinated organic by-products are hygienically and environmentally objectionable. Their adequate separation from the acetaldehyde product and from other gas and liquid streams which exit the process and their proper destruction or disposal add to the operating costs of the manufacturing processes.
These chlorinated organic by-products have a number of mechanistic origins. Some result from direct additions of hydrochloric acid to ethylene, giving ethylchloride, and to olefinic by-products. Others result from palladium centered oxychlorination, for example, 2-chloroethanol from ethylene. The predominant origin of chlorinated organic by-products is oxychlorination by cupric chloride, most arise from copper centered oxychlorination of acetaldehyde, giving chloroacetaldehydes, and further reactions of the chloroacetaldehydes. Accordingly, we determined that most of the objectionable chlorinated organic by-product yield results not simply from the presence of chloride, but from the combination of chloride and copper.
Aqueous palladium(II) salts also oxidize higher olefins to carbonyl compounds according to equation (11), where R, R', and R" are hydrocarbyl substituent groups and/or hydrogen (R=R'=R"=H for ethylene): ##STR2##
As examples, aqueous palladium(II) salts oxidize propylene to acetone (and some propionaldehyde), butenes to methyl ethyl ketone (and some butyraldehyde), and cyclohexene to cyclohexanone. Higher olefins can be oxidized by dioxygen using the Wacker system, but serious problems encountered in using the Wacker system to oxidize higher olefins have effectively prohibited any other significant application to manufacturing carbonyl compounds.
The rate of oxidation of the olefinic double bond by aqueous palladium(II) salts generally decreases as the number and/or size of hydrocarbyl substituents increases. This decrease in rate is particularly severe with PdCl.sub.4 = in the Wacker system, due to the competition of chloride with the more weakly binding higher olefins for palladium(II) complexation and due to the lowered electrophilicity of multiply chloride-bound olefin-palladium(II) intermediates. Consequently, much higher palladium concentrations (with its concomitant palladium investment) are necessary to obtain volumetric production rates of higher carbonyl compounds comparable to acetaldehyde production rates.
An even more prohibitive disadvantage of the Wacker system for manufacturing carbonyl compounds from higher olefins is the substantially increased production of chlorinated organic by-products. Higher olefins are more susceptible to palladium centered oxychlorination, which chlorinates not only at olefinic carbon atoms but also at allylic carbon atoms. Higher aldehydes and ketones having methylene groups adjacent to the carbonyl group are also more susceptible to cupric chloride mediated oxychlorination than is acetaldehyde. As a result, the productivity of the Wacker system for producing chlorinated organic by-products increases rapidly both with increasing number and size of hydrocarbyl substituents in the olefin.
Other, multistep manufacturing processes are typically used instead of the Wacker process to convert higher olefins into corresponding carbonyl compounds. For example, the manufacture of methyl ethyl ketone (2-butanone) involves the reaction of n-butenes with concentrated sulfuric acid to produce sec-butyl hydrogen sulfate and hydrolysis of sec-butyl hydrogen sulfate to obtain 2-butanol and diluted sulfuric acid. 2-butanol is catalytically dehydrogenated to produce methyl ethyl ketone. The diluted sulfuric acid must be reconcentrated for recycle.
Other carbonyl compounds are instead manufactured from starting materials more expensive than the corresponding higher olefin. For example, cyclopentanone is manufactured from adipic acid instead of from cyclopentene.
An effective method for the direct oxidation of higher olefins to carbonyl compounds by dioxygen has been long sought in order to enable more economical manufacturing of carbonyl compounds. Yet, in 30 years since the development of the Wacker system, no alternate palladium-based system for the oxidation of olefins by dioxygen which avoids the disadvantages and limitations of the Wacker system has been successfully applied in commercial manufacturing operation.
Systems have been proposed which use polyoxoanions, instead of cupric chloride, in combination with palladium to effect the oxidation of olefins.
U.S. Pat. No. 3,485,877, assigned to Eastman Kodak Company (hereafter, "Eastman patent") discloses a system for converting olefins to carbonyl compounds by contacting with an agent comprising two components, one of which is palladium or platinum, and the other is molybdenum trioxide or a heteropolyacid or salt thereof. This patent discloses that the so-called "contact agent" may be in an aqueous solution for a liquid phase process, but that it is advantageous and preferred to support the agent on a solid carrier for a vapor phase process in which gaseous olefin is contacted with the solid phase agent. The patent compares the oxidation of propylene with a liquid phase contact agent (in Example 16), to give acetone substantially free of by-products with the oxidation of propylene in the vapor phase with a corresponding solid contact agent (in Example 10), to give acrolein. Apparently, the behavior of an olefin's liquid phase reaction with the disclosed aqueous contact agent solution cannot be predicted from the behavior of the olefin's vapor phase reaction with the analogous solid contact agent.
Eastman patent discloses that, when operating in the liquid phase, heteropolyacids or their salts, and particularly phosphomolybdic acid or silicomolybdic acid in water are preferred. Among the heteropolyacids disclosed, only phosphomolybdic acid and silicomolybdic acid are demonstrated by working example. No salts of heteropolyacids are so demonstrated. Phosphomolybdovanadic acid or salts thereof are nowhere mentioned in this patent.
Eastman patent also discloses the reaction in the presence of oxygen or oxygen containing gas. It also discloses periodic regeneration of the contact agent with air. However, the use of oxygen or air is demonstrated by working examples only for reactions of olefins in the vapor phase with solid phase contact agents.
We have found that oxygen reacts too slowly with reduced phosphomolybdic acid or silicomolybdic acid in aqueous solutions for such solutions to be practically useful in the industrial conversion of olefins to carbonyl compounds using oxygen or air as oxidant. In contrast, our reduced polyoxoanions comprising vanadium in aqueous solution of the present invention can react rapidly with oxygen or air.
In addition, Eastman patent discloses palladium chlorides among various preferred palladium or platinum components for the contact agent. Palladous chloride is predominantly used among the working examples. Eastman patent also discloses that it is possible to improve the action of the contact agent by incorporating small amounts of hydrochloric acid or ferric chloride. However, the only demonstration by working example adds ferric chloride in a solid phase contact agent for a vapor phase reaction (Example 19) to obtain higher reaction rates (conversion and space time yield). No such demonstration, nor result, is given for addition of hydrochloric acid to either a solid or a liquid phase contact agent, nor for addition of either hydrochloric acid or ferric chloride to a liquid phase contact agent.
Belgian Patent No. 828,603 and corresponding United Kingdom Patent No. 1,508,331 (hereafter "Matveev patents") disclose a system for the liquid phase oxidation of olefins employing an aqueous solution combining: a) a palladium compound; b) a reversible oxidant which has a redox potential in excess of 0.5 volt and which is a mixed isopolyacid or heteropolyacid containing both molybdenum and vanadium, or a salt of said polyacid; and, c) an organic or mineral acid other than said mixed isopolyacid or heteropolyacid, which organic or mineral acid is free of halide ions and is unreactive (or at most weakly reactive) with the palladium compound. The disclosed system differs from that of Eastman patent by simultaneously employing only certain heteropolyacids and mixed isopolyacids and adding certain other acids to the solution. Those certain polyacids employed contain both molybdenum and vanadium. Those certain other acids added are not the polyacid and are free of halide ions.
Matveev patents disclose that only the certain polyacids, containing both molybdenum and vanadium, function satisfactorily in the system as reversibly acting oxidants, wherein the reduced form of the oxidant is reacted with dioxygen to regenerate the oxidant. The patent further discloses that the polyacid used contains from 1 to 8 vanadium atoms, more preferably 6 atoms, in a molecule with molybdenum. According to the disclosure, as the number of vanadium atoms increases from 1 to 6 the principal characteristics of the catalyst, such as its activity, stability, and olefin capacity, increase.
Matveev patents disclose typical heteropolyacids of a formula H.sub.n [PMo.sub.p V.sub.q O.sub.40 ], in which n=3+q, p=12-q, q=1 to 10. Matveev patents disclose that the catalyst is prepared, in part, by dissolving in water, oxides, salts, and/or acids of the elements forming the polyacid and then adding to the solution, the specified other organic or mineral acid. A preferred catalyst is said to be prepared by dissolving in water Na.sub.3 PO.sub.4 (or Na.sub.2 HPO.sub.4, or NaH.sub.2 PO.sub.4, or H.sub.3 PO.sub.4, or P.sub.2 O.sub.5), MoO.sub.3 (or Na.sub.2 MoO.sub.4, or H.sub.2 MoO.sub.4), V.sub.2 O.sub.5 (or NaVO.sub.3), and Na.sub.2 CO.sub.3 (or NaOH) to form a solution, adding PdCl.sub.2 to the solution of molybdovanadophosphoric acid, and then adding the other acid. (Sulfuric acid is the only such acid demonstrated by working example.) It is said to be best if the total number of Na atoms per atom of P is not less than 6. Heteropolyacids in the series designated H.sub.4 [PMo.sub.11 VO.sub.40 ] to H.sub.11 [PMo.sub.4 V.sub.8 O.sub.40 ] are said to be obtained, and are said to be used in most of the working examples. (We have found that such solutions prepared according to the methods disclosed in Matveev patents are not actually solutions of free heteropolyacids, as designated by formulas of the type H.sub.n [PMo.sub.p V.sub.q O.sub.40 ]. Instead, they are solutions of sodium salts of partially or completely neutralized heteropolyacids; that is, solutions of sodium polyoxoanion salts.)
According to Matveev patents, the activity and stability of the catalyst is increased by the presence of certain other mineral or organic acids which do not react (or react only feebly) with palladium and contain no halide ions(e.g. H.sub.2 SO.sub.4, HNO.sub.3, H.sub.3 PO.sub.4, or CH.sub.3 COOH). The most preferable of the above acids is sulfuric acid, which is said to increase the activity and stability of the catalyst whilst not seriously increasing the corrosivity of the solution. Sulfuric acid is the only acid which appears in the working examples. Matveev patents prescribe that the amount of acid is enough to maintain the "pH" of the solution at "not more than 3, preferably at 1.0". The working examples predominantly recite "pH" 1. Matveev patents indicate that with "higher pH values", the catalyst is not sufficiently stable with respect to hydrolysis and palladium precipitation, and is of low activity in the olefinic reaction. They further indicate that with "lower pH values", the rate of the oxygen reaction is appreciably diminished. However, Matveev patents do not disclose any method for determining the "pH" of the disclosed solutions, nor do they specify anywhere how much sulfuric acid was added to achieve the stated "pH" value.
The disclosure of Matveev patents is generally directed towards providing a catalyst system having a reversibly acting oxidant (wherein the reduced form of the oxidant can be reacted with dioxygen to regenerate the oxidant) and having an absence of chloride ions. Mineral acids which contain halide ions are specifically excluded from the certain other acids added in the disclosed system. PdCl.sub.2 is among the palladium compounds used in the working examples; it is the only source of added chloride disclosed and is added only coincidental to the selection of PdCl.sub.2 as the palladium source. PdCl.sub.2 and PdSO.sub.4 are generally disclosed to be equivalent palladium sources.
Matveev patents' preferred palladium concentration in the catalyst is said to be 0.002 g-atom/liter (2 millimolar). This is the concentration demonstrated in most of the working examples. In Example 9 of both Belgian and British patents, a catalyst containing a very high concentration of heteropolyacid, 1.0 g-mole/liter, and a very high concentration of PdCl.sub.2, 0.5 g-atom/liter, is disclosed. This would mean that 1.0 g-atom/liter chloride is added as part of the palladium source. The stated conclusion from this example is that the high viscosity and specific gravity of such concentrated solutions adversely affect the mass transfer conditions and make the process diffusion controlled and impractical. The result reported for this test with 0.5 g-atom/liter PdCl.sub.2 is so poor, especially in terms of palladium activity (see Table 1), as to lead one away from attempting to use the example.
The results of selected working examples reported in Matveev patents are presented in Table 1. The examples selected are those said to use a phosphomolybdovanadic heteropolyacid in the oxidation of ethylene for which quantitative results are reported. Data and results to the left of the vertical bar in Table 1 are taken directly from the patent. Results to the right of the vertical bar are calculated from the reported results. The Example numbers are those used in Belgian 828,603.
Most working examples in Matveev patents report tests conducted in a shaking glass reactor. Typical reaction conditions in this reactor were 90.degree. C. with 4.4 psi of ethylene, and separately with 4.4 psi of oxygen. Among the examples collected in Table 1, those using the shaking glass reactor with the preferred concentrations of heteropolyacid and palladium (Examples 1-6) gave ethylene and oxygen rates of 0.089-0.156 and 0.037-0.086 (millimoles/liter)/second, respectively (see Table 1). Example 9, with 0.5 g-atom/liter PdCl.sub.2, is said to be diffusion controlled; ethylene and oxygen reaction rates were 0.223 and 0.156 (millimoles/liter)/second, respectively.
We have found that shaking reactors are generally poor devices for mixing such gaseous reactants and liquid aqueous phases and the rate diffusion (mass transfer) of gaseous reactants into an aqueous catalyst solution for reaction is prohibitively slow in such reactors. Additionally, 4.4 psi of ethylene is relatively too low a pressure for rapid dissolution of ethylene into a aqueous catalyst solution.
TABLE 1 __________________________________________________________________________ Examples from Belgian Patent 828,603 __________________________________________________________________________ Reported: C.sub.2 H.sub.4 C.sub.2 H.sub.4 O.sub.2 Ex..sup.1 [Pd].sup.3 Pd [HPA].sup.4 HPA % xs temp P.sub.C.sbsb.2.sub.H.sbsb.4 rate capacity P.sub.O.sbsb.2 rate No. Rctr.sup.2 mM source Molar Vq.sup.5 V.sup.6 .degree.C. mm Hg W.sup.9 mole/l mm Hg W.sup.10 __________________________________________________________________________ 1 sg 2 PdCl.sub.2 0.3 6 25 90 230 143 0.6 230 115 2 sg 2 PdCl.sub.2 0.3 8 35 90 230 248 0.8 230 3 sg 2 PdSO.sub.4 0.3 4 15 90 230 128 0.36 230 105 4 sg 2 PdCl.sub.2 0.3 3 10 90 230 120 0.25 230 70 5 sg 2 PdSO.sub.4 0.3 2 5 90 230 210 0.15 230 50 6 sg 2 PdCl.sub.2 0.2 6 25 90 230 190 0.3 230 60 6 sg 2 PdCl.sub.2 0.2 6 25 110 6 atm 900 0.3 3.5 atm 450 9 sg 500 PdCl.sub.2 1.0 6 25 90 230 300 3.0 230 210 10 sg 1 Pd metal 0.2 6 25 90 230 150 0.2 230 100 12 sg 1 PdSO.sub.4 0.1 5 ? 50 230 25 0.15 230 10 __________________________________________________________________________ Calculated: C.sub.2 H.sub.4 Pd O.sub.2 Ex..sup.1 P.sub.C.sbsb.2.sub.H.sbsb.4 rate t.f. Pd % V P.sub.O.sbsb.2 rate No. psi mM/s.sup.11 1/s.sup.12 TON.sup.7 red.sup.8 psi mM/s.sup.13 __________________________________________________________________________ 1 4.4 0.106 0.053 300 53 4.4 0.086 2 4.4 0.185 0.093 400 49 4.4 ? 3 4.4 0.095 0.048 180 52 4.4 0.078 4 4.4 0.089 0.045 125 51 4.4 0.052 5 4.4 0.156 0.078 75 48 4.4 0.037 6 4.4 0.141 0.071 150 40 4.4 0.045 6 88.2 0.670 0.335 150 40 51.4 0.335 9 4.4 0.223 0.0004 6 80 4.4 0.156 10 4.4 0.112 0.112 200 27 4.4 0.074 12 4.4 0.019 0.187 150 150? 4.4 0.007 __________________________________________________________________________ 1. All examples use solutions said adjusted to pH 1 with sulfuric acid, except Ex. 12 in which no sulfuric acid is added and the pH is not reported. 2. Reactor type: sg = shaking glass, ss = stainless steel (method of agitation not reported) 3. Palladium concentration, millimolar (mgatom/liter) 4. Heteropolyacid concentration, Molar (gmole/liter) 5. Heteropolyacid said to be used, according to the formula H.sub.n [PMo.sub.p V.sub.q O.sub.40 ], n = 3 + q, p = 12 - q 6. Vanadium used in excess in the preparation of the HPA solution, % of q (see footnote 5) 7. Palladium turnover number per ethylene reaction = (C.sub.2 H.sub.4 capacity, moles/liter)/(Pd concentration, moles/liter) 8. Fraction of vanadium reduced (utilized to oxidize ethylene) in ethylen reaction = (C.sub.2 H.sub.4 capacity,mole/l)/[(total V concentration,gatom/l)/2], where total V concentration = [HPA](q)(1 + fraction excess V used in HPA solution preparation) 9. Average rate of ethylene reaction as [(milliters C.sub.2 H.sub.4 at 75 mmHg, 23.degree. C.)/liter solution]/minute. 10. Average rate of oxygen reaction as [(milliters O.sub.2 at 750 mmHg, 23.degree. C.)/liter solution]/minute. 11. Rate of ethylene reaction as [millimoles C.sub.2 H.sub.4 /liter solution/second. 12. Palladium turnover frequency, {[millimoles C.sub.2 H.sub.4 /liter solution]/second}/millimolar Pd concentration. 13. Rate of oxygen reaction as [millimoles O.sub.2 /liter solution]/second.
One test in Example 6 is reported for another reactor, a stainless steel reactor, with 88.2 psi of ethylene and with 51.4 psi of oxygen, each at 110.degree. C. The method of mixing the gas and liquid phases in this reactor is not specified. Example 6 also reports results with the same catalyst system in the shaking glass reactor. The ethylene reaction rates were 0.141 (millimoles/liter)/second in the shaking glass reactor and 0.670 (millimoles/liter)/second in the stainless steel reactor. The oxygen reaction rates were 0.045 (millimoles/liter)/second in the shaking glass reactor and 0.335 (millimoles/liter)/second in the stainless steel reactor. Thus, the reaction rates did not increase proportionally with the pressure when it was increased from about 4 psi to about 90 psi. It is well known that the diffusion rate of a reacting gas into a liquid, as well as the gas molecule concentration in the liquid phase at saturation, is proportional to the partial pressure of the gas in the gas phase, all other factors being constant. Accordingly, the stainless steel reactor used for the higher pressure test of Example 6 appears to be a poorer device for the mixing of gas and liquid phases than the shaking glass reactor used for the other test in the Matveev patents.
Typical apparent palladium turnover frequencies calculated from ethylene reaction rates and palladium concentrations reported in Matveev patents' working examples using a shaking glass reactor are all less than 0.2 (millimoles C.sub.2 H.sub.4 /mg-atom Pd)/second. The higher pressure test at 110.degree. C. in a stainless steel reactor in Example 6 gave the highest apparent palladium turnover frequency of 0.335 (millimoles C.sub.2 H.sub.4 /mg-atom Pd)/second. Although Matveev patents purport that the disclosed catalysts are up to 30 to 100 times more active in olefin oxidation over the Wacker catalyst, the apparent activity of the palladium catalyst in the best example is no higher than the activity of a typical Wacker palladium catalyst in typical process operation at comparable temperatures. This result is obtained even though the disclosed catalyst solution is substantially free of the chloride ion concentration which inhibits the palladium activity in the Wacker catalyst. In contrast, the present invention demonstrably provides palladium catalyst activities substantially exceeding the activity of a Wacker palladium catalyst in typical process operation.
From Matveev patents' ethylene reaction capacities and the palladium concentrations, the number of palladium turnovers per ethylene reaction capacity can be calculated (see Table 1, TON). The highest number of turnovers obtained was 400 with the heteropolyacid containing 8 vanadium atoms (and with 35% excess vanadium present), Example 2.
The ethylene reaction capacities of the catalyst solutions of Matveev's working examples appear generally to follow the vanadium content of the solutions (see Table 1). For the tests with the preferred concentrations of heteropolyacid and palladium and at the preferred "pH" 1 (Examples 1-6), the reported ethylene reaction capacities are calculated to correspond to 40% to 53% of the oxidizing capacity of the vanadium(V) content of the solution, assuming two vanadium(V) centers are reduced to vanadium(IV) for each ethylene oxidized to acetaldehyde.
Example 12 of Matveev's Belgian patent reports a test with no addition of sulfuric acid. (This result was omitted from the UK patent.) The heteropolyacid is designated H.sub.5 [PMo.sub.10 V.sub.2 O.sub.40 ] and is used at 0.1 molar concentration with palladium sulfate at 0.1 mg-atom/liter concentration. A "pH" for this solution is not reported. The reaction is conducted at 50 C. On cycling between ethylene and oxygen reactions, the rate of the ethylene reaction is said to diminish constantly due to hydrolysis of the Pd salt. (Typical examples with sulfuric acid added, such as examples 1-6, were reported stable to 10 or more cycles.) This result corresponds to Matveev's disclosure that the stability of the catalyst is increased by sulfuric acid, that the amount of acid is such as to maintain the "pH" at not more than 3, and that with higher "pH" values the catalyst is not sufficiently stable against hydrolysis and palladium precipitation. This result reported with no addition of sulfuric acid is so poor as to lead one away from attempting to use the example.
Matveev patents also report working examples for the oxidation of propylene to acetone, n-butenes to methyl ethyl ketone, and 1-hexene to methyl butyl ketone using the disclosed catalyst system. For reaction of mixtures of n-butenes, 4.4 psi, at 90.degree. C. in the shaking glass reactor (Example 19 in Belgian 828,603; Example 16 in UK 1,508,331), the reported reaction rate is 50 [(ml butenes at 750 mm Hg, 23.degree. C.)/liter]/minute (corresponding to 0.037 (millimoles butenes/liter)/second) an the capacity of the reaction solution is 0.25 moles butenes/liter. The palladium concentration in the example is 2 mg-atom/liter: the palladium turnover frequency is calculated 0.019 (millimoles butenes/mg-atom Pd)/second; the number of Pd turnovers per butene reaction capacity is calculated 125. The fraction of the vanadium(V) concentration of the solution reduced by the butene capacity is calculated 51%.
In contrast to the teachings of the Matveev patents, we have found the following: 1) Although the Matveev patents teach that sulfuric acid increases the activity and stability of the catalyst, we have discovered that substantially increased activity (olefin and oxygen reaction rates) and stability can be obtained by avoiding the presence of sulfuric acid, and of sulfate species generally; 2) Although the Matveev patents teach that the rate of the oxygen reaction is appreciably diminished at "pH" values lower than 1, we have discovered that oxygen reaction rates can be obtained which are orders of magnitude higher than those reported in the patents and which are substantially undiminished in solutions having hydrogen ion concentrations greater than 0.10 mole/liter; 3) Although the Matveev patents teach that the activity and stability of the catalyst are increased on increasing the number of vanadium atoms in the polyacid, for example from 1 to 6, we have discovered that, at least in the practice of the present inventions, the activity (olefin and dioxygen reaction rates) is typically invariable with the vanadium content of the polyacid and the stability may be decreased on increasing the vanadium content of the polyacid towards 6; 4) Although the Matveev patents teach that the total number of Na atoms per atom of P be not less than 6, we have found that with the preferred polyoxoanion-comprising catalyst solutions of the present invention, which optionally contain Na.sup.+ countercations, the desired acidity can be obtained while avoiding sulfuric acid by preferably keeping the number of Na atoms per atom of P less than 6.
East German Patent No. 123,085, by some of the inventors of the Matveev patents, discloses a chloride-free catalyst for the liquid phase oxidation of ethylene to acetaldehyde and acetic acid that consists of a solution of a palladium salt with an anion that does not complex palladium or does so only weakly and a heteropolyacid or isopolyacid or salts thereof that have a redox potential greater than 0.35 V. The aqueous solutions disclosed in the Examples contain 2.5.times.10.sup.-4 mole/liter PdSO.sub.4, 5.times.10.sup.-2 mole/liter heteropolyacid, (specified as H.sub.5 [P(Mo.sub.2 O.sub.7).sub.5 V.sub.2 O.sub.6 ], H.sub.8 [Si(Mo.sub.2 O.sub.7)V.sub.2 O.sub.6 ], or H.sub.8 [Ge(Mo.sub.2 O.sub.7)V.sub.2 O.sub.6 ]), 5.times.10.sup.-2 mole/liter CuSO.sub.4 (omitted in Example 3), and 5.times.10.sup.-2 mole/liter NaVO.sub.3, and are said to have a "pH" of 2. Neither the method of preparation of the heteropolyacids in the solutions, nor the means of acidifying the solutions to this stated "pH" is disclosed. In the Examples, these solutions are said to be reacted at 30.degree. C. with ethylene at 720 mm Hg partial pressure or at 60.degree. C. with ethylene at 600 mm Hg partial pressure, and with oxygen at the same pressures, using a glass reactor that can be agitated. The greatest ethylene reaction rate disclosed is 44 ml ethylene reacted by 50 ml solution in 20 minutes at 60.degree. C. with and ethylene partial pressure of 600 mm Hg, corresponding to 0.21 (millimole C.sub.2 H.sub.4 /liter)/second and a palladium turnover frequency of 0.085 (millimole C.sub.2 H.sub.4 /mg-atom Pd)/second. The greatest oxygen reaction rate disclosed is 10 ml oxygen reacted by 50 ml solution in 27 minutes at 30.degree. C. with an oxygen partial pressure of 720 mm Hg, corresponding to 0.005 (millimole O.sub.2 /liter)/second.
East German Patent No. 123,085, also mentions small additions of chloride or bromide ions act as oxidation accelerators and activate the catalysts, with molar ratios of [Pd.sup.++ ]:[Cl.sup.- ].ltoreq.1:20 and [Pd.sup.++ ]:[Br.sup.- ].ltoreq.1:5 being favorable. The patent makes no other mention of chloride addition to the disclosed catalyst and chloride is nowhere indicated in any of the working Examples. Instead, the title of the patent, the claims, and the disclosure elsewhere all explicitly specify a chloride-free catalyst.
Additional results from some of the inventions of the Matveev patents are reported in Kinetika i Kataliz, vol. 18(1977), pp. 380-386 (English translation edition pp. 320-326, hereafter "Kinet. Katal. 18-1"). Reaction kinetic experiments are reported for the ethylene oxidation reaction with phosphomolybdicvanadic heteropolyacids in the presence of Pd(II) sulfate using a shaking reactor with circulation of the gas phase. The absolute values of the observed reaction rates are said to be quite small, and not complicated by mass-transfer processes. Most of the reported experiments are conducted at about 20.degree. C., and this low temperature appears to be the principal reason the observed reaction rates are so small. Typical reaction rates reported are about 1 to 12.times.10.sup.-4 (moles/liter)/minute, which corresponds to about 0.002 to 0.020 (millimoles/liter)/second; compare to ethylene reaction rates of about 0.1-0.2 (millimoles/liter)/second calculated from the results reported for experiments at 90.degree. C. in Matveev patents (see Table 1). The reaction rates reported in Kinet. Katal. 18-1 are so small as to lead one away from attempting to use the reported reaction conditions for any practical production purpose.
Ethylene pressures for the reactions of Kinet. Katal. 18-1 are not reported. The ethylene concentrations are instead given, but no method of either setting or determining the ethylene concentration is mentioned, nor is it clear whether these ethylene concentrations are sustained in solution under the reaction conditions.
Kinet. Katal. 18-1 states that solutions of phosphomolybdicvanadic heteropolyacids were synthesized by a procedure described in Zh. Neorg. Khim., vol. 18(1973), p. 413 (English translation edition pp. 216-219). This reference describes making solutions from Na.sub.2 HPO.sub.4, Na.sub.2 MoO.sub.4 .multidot.2H.sub.2 O, and NaVO.sub.3 .multidot.2H.sub.2 O at "pH" 2; the method of acidification of the solutions of these basic salts, when stated, is with sulfuric acid. (This reference further mentions the isolation of crystalline vanadomolybdo-phosphoric acids via ether extraction of their ether addition compounds from sulfuric acid-acidified solutions. These methods of preparing solution vanadomolybdophosphoric acids with sulfuric acid and crystalline products by ether extraction are also described in earlier papers cited by this reference; for example, Inorg. Chem., 7 (1968), p. 137.) The reaction solutions of Kinet. Katal. 18-1 are said to be prepared from the solutions of phosphomolybdicvanadic heteropolyacids by addition palladium sulfate, dilution, and adjustment of the pH by the addition of H.sub.2 SO.sub. 4 or NaOH. However, this reference does not disclose the composition of the test solutions, in terms of the amounts of H.sub.2 SO.sub.4 or NaOH added, nor any method for determining the pH of the disclosed solutions.
Kinet. Katal. 18-1 reports the dependence of the ethylene reaction rate on the solution pH over the stated range 0.8 to 2.2, under the disclosed conditions with the heteropolyacid designated H.sub.6 [PMo.sub.9 V.sub.3 O.sub.40 ] at 0.05 mole/liter, palladium at 3.times.10.sup.-3 g-atom/liter, ethylene at 1.times.10.sup.-4 mole/liter, and 21.degree. C. As the pH is increased towards 2, the rate of the ethylene reaction is shown to decrease. From evaluation of graphic figures in the reference, the maximum rate of ethylene reaction was achieved over a pH range of 0.8 to 1.6, and corresponded to 0.023 (millimole C.sub.2 H.sub.4 /liter)/second and a palladium turover frequency of 078 (mole C.sub.2 H.sub.4 /mole palladium)/second.
Matveev reviews his studies on the oxidation of ethylene to acetaldehyde in Kinetika i Kataliz, vol. 18 (1977), pp. 862-877 (English translation edition pp. 716-727; "Kinet. Katal. 18-2"). The author states (English translation edition p. 722): "The chloride-free catalyst was an aqueous solution of one of the HPA-n, acidified with H.sub.2 SO.sub.4 to pH 1, in which a nonhalide palladium salt (sulfate, acetate, etc.) was dissolved." (HPA-n are defined as phosphomolybdenumvanadium heteropolyacids.) Reference is then made to the studies reported in Kinet. Katal. 18-1.
Reaction Kinetics and Catalysis Letters, vol 16 (1981), pp. 383-386 reports oxidation of 1-octene to 2-octanone using a catalytic system of PdSO.sub.4 and heteropolyacid designated H.sub.9 PMo.sub.6 V.sub.6 O.sub.40 in a shaking glass reactor with 1 atm. oxygen. The heteropolyacid is said to be synthesized as in UK 1,508,331, and used as an acidic sodium salt Na.sub.7 H.sub.2 PMo.sub.6 V.sub.6 O.sub.40. The catalyst solution is said to have a pH equal to 0.5-1.0, which was attained by the addition of H.sub.2 SO.sub.4. However, no results are identified with a specific pH value. Palladium is used in concentrations of .about.4-6 millimolar and PdSO.sub.4 is said to give a more active catalyst than PdCl.sub.2. The catalyst is said to have limited stability above 80.degree. C., apparently due to precipitation of palladium.
Ropa Uhlie 28, pp. 297-302 (1986) (Chem Abstr. 107(1):6740r) reports oxidation of 1-octene to 2-octanone using a solution of 0.075 M heteropolyacid designated H.sub.3+n PMo.sub.12-n V.sub.n O.sub.40, n=6 or 8, and containing PdSO.sub.4. The heteropolyacid solution was prepared from NaH.sub.2 PO.sub.4, MoO.sub.3, and V.sub.2 O.sub.5 in water by addition of NaOH, then H.sub.2 SO.sub.4, with adjustment of the stated "pH" to 1.
J. Organomet. Chem. 327 (1987) pp. C9-C14 reports oxidation of 1-octene to 2-octanone by oxygen using an aqueous solution of 0.12 mole/liter heteropolyacid designated HNa.sub.6 PMo.sub.8 V.sub.4 O.sub.40, with 0.01 mole/liter PdSO.sub.4, with various co-solvents, at 20.degree. C., in one-stage mode. The heteropolyacid is said to be prepared by the method described in UK 1,508,331; the "pH" of the catalyst solution is not specifically disclosed. For the reaction, 1-octene and oxygen are contacted simultaneously with the catalyst solution. The heteropolyacid cocatalyst is said to be regenerated by treating the aqueous solution with 1 atm. O.sub.2 at 75.degree. C.
Reaction Kinetics and Catalysis Letters, vol 3 (1975), pp. 305-310 reports the oxidation of vanadium(IV) in aqueous solutions of vanadyl sulfate (V.sup.IV OSO.sub.4), 0.05-0.25 mole/liter, in the "pH" region 2.5-4.5, in the presence of small amounts of sodium molybdate in a shaker reactor, at 30.degree. C. with 730 mmHg oxygen pressure. At "pH" values below 3.0 the reaction rate is reported to decrease sharply. A heteropolyacid complex of molybdenum and vanadium was isolated from a reaction solution.
Koordinatsionnaya Khimiya, vol. 3 (1977), pp. 51-58 (English translation edition pp. 39-44) reports the oxidation of reduced phosphomolybdovanadium heteropolyacids containing vanadium(IV), in aqueous solution at "pH"'s&lt;1, at 60.degree. C. by oxygen. Heteropolyacids designated H.sub.3+n [PMo.sub.12-n V.sub.n O.sub.40 ], n=1-3, were said to be synthesized by the method of Zh. Neorg. Khim., vol. 18 (1973), p. 413 (see above), and a solution of the sodium salt of the heteropolyacid designated n=6 was said to be prepared by dissolving stoichiometric amounts of sodium phosphate, molybdate, and vanadate in water, boiling the solution, and acidifying it to "pH" 1. Different "pH" values for the solutions of the reduced forms of these heteropolyacids were said to be obtained by altering the initial "pH" values of the heteropolyacid solutions, monitored by a pH meter. The acid used for acidification and for altering the initial "pH" values are not disclosed. Oxygen reaction rates for the reduced forms of the heteropolyacids designated n=2,3, and 6 show maxima at about "pH" 3 (at about 34.times.10.sup.-3 (mole/liter)/minute; or, 0.57 (millimole/liter)/second), and decline precipitously as the "pH" is lowered; it becomes almost negligible for n=2 at "pH" 1.
Koordinatsionnaya Khimiya, vol. 5 (1979), pp. 78-85 (English translation edition pp. 60-66) reports the oxidation of vanadium(IV) in aqueous solutions of vanadyl sulfate, 0.1-0.4 mole/liter, in the "pH" region 2.5-4.5, in the presence of smaller amounts of molybdovanadophosphoric heteropolyacid designated H.sub.9 PMo.sub.6 V.sub.6 O.sub.40, in an agitated reactor, at 0.degree.-30.degree. C., by oxygen. A weak dependence of the rate on "pH" is reported, with the rate decreasing with decreasing "pH" below about "pH" 3.5. The addition of Na.sub.2 SO.sub.4 is said to have no influence on the rate of the reaction.
Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1981, pp. 2428-2435 (English translation edition pp. 2001-2007) reports studies of the oxidation of reduced forms ("blues") of molybdovanadophosphate heteropolyacids designated H.sub.3+n [PMo.sub.12-n V.sub.n O.sub.40 ], n=1-4,6, containing vanadium(IV), in aqueous solution at "pH" 3.0, in a glass flask with magnetically-coupled stirring of the liquid phase, at 25.degree. C. with 2-10 kPa (0.3-1.5 psi) oxygen. Reaction rates are extremely slow under these low temperature, low pressure conditions in this reaction mixing vessel. (From the data, reaction rates in the region &lt;0.0001 (millimoles/liter)/second are calculated.) The oxygen reaction rates of a reduced form of the molybdovanadophosphate n=3 were measured at "pH"'s 2.0,3.0, and 4.0. A maximum was observed at "pH" 3.0. Aqueous solutions of Na salts of the heteropolyacids and the corresponding blues for the experiments were said to be obtained as in Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1980 , pp. 1469. This reference discloses that aqueous solutions of heteropolyanions were obtained by reacting stoichiometric amounts of H.sub.3 PO.sub.4, MoO.sub.3, and NaVO.sub.3 .multidot.2H.sub.2 O with heating in the presence of Na.sub.2 CO.sub.3. (Neither the amount of Na.sub.2 CO.sub.3 added, the concentration of heteropolyanion, the resulting "pH"'s, nor the complete compositions of the solutions are disclosed.) This reference further discloses the addition of vanadium(IV) in the form of VOSO.sub.4 .multidot.2H.sub.2 O to produce the heteropoly blues. The experimental solutions in this reference are said to comprise heteropolyanion and vanadyl at "pH" 1.60-2.98, buffer solution of NaHSO.sub.4 and Na.sub.2 SO.sub.4 ; neither the concentration of the buffering sulfate ions nor an accounting of their origin is disclosed.
Reaction Kinetics and Catalysis Letters, vol 17 (1981), pp. 401-406 reports the oxidation of vanadium(IV) in aqueous solutions of vanadyl sulfate, 0.02-0.4 mole/liter, in the "pH" region 2.5-4.5, in the presence of smaller amounts of molybdovanadophosphoric heteropolyacid designated H.sub.6 PMo.sub.9 V.sub.3 O.sub.40, by the methods of Koordinatsionnaya Khimiya, vol. 5 (1979), pp. 78-85. At "pH" values below 3.0 the reaction rate is reported to decrease sharply.
J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 reports studies of the palladium sulfate-catalyzed oxidation of 1-butene to 2-butanone (methyl ethyl ketone) with phosphomolybdovanadic acids both in the absence and in the presence of oxygen. These studies are reported in greater detail in Palladium and Heteropolyacid Catalyzed Oxidation of Butene to Butanone, S.F. Davison, Ph.D. Thesis, University of Sheffield, 1981. These references report, as do others loc. cit., that phosphomolybdovanadic acids are extremely complex mixtures of anions of the type [PMo.sub.12-x V.sub.x O.sub.40 ].sup.(3+x)-. Crystalline phosphomolybdovanadic acids, designated H.sub.3+n [PMo.sub.12-n V.sub.n O.sub.40 ], n=1-3, prepared by the ether extraction method of Inorg. Chem., 7 (1968), p. 137 were observed to be mixtures which disproportionated still further in the acidic media used for catalysis. Accordingly, solutions prepared by the method of UK 1,508,331 were chosen as appropriate for the catalytic reactions (see Davison Thesis, pp. 63 and 77), except that stoichiometric amounts of V.sub.2 O.sub.5 (not excess) were used. The solutions were prepared from V.sub.2 O.sub.5, MoO.sub.3, Na.sub.3 PO.sub.4 .multidot.12H.sub.2 O, and Na.sub.2 CO.sub.3, at 0.2 M P, and acidified to "pH" 1 by addition of concentrated sulfuric acid
The reactions of J. Chem. Soc. Dalton Trans,. 1984, pp. 1223-1228 and Davison Thesis in the absence of oxygen were conducted at 20.degree. C. and 1 atm 1-butene in a mechanically shaken round-bottomed flask. Reactions using 5 mM PdSO.sub.4 and 0.05 M vanadium(V) in aqueous sulfuric acid (0.03-0.2 mole/liter, depending on n) are reported to give similar initial reaction rates for n=1-7. The reactions required ca. 30 minutes for completion and gave 5 turnovers on Pd (stoichiometric for two vanadium(V) reduced to vanadium(IV) per 1-butene oxidized to 2-butanone.). A stated intention of the work was to minimize chloride content; PdCl.sub.2 is said to have similar reactivity to PdSO.sub.4.
The reactions of J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 and Davison Thesis in the presence of oxygen were conducted at 20.degree. C. and 1 atm of 1:1 1-butene:oxygen in a round-bottomed flask with magnetically coupled stirring. Results are reported for the solutions used in reactions in the absence of oxygen; up to about 40 turnovers on Pd were obtained in about 120 minutes with the heteropolyacid designated PMo.sub.6 V.sub.6 (H.sub.9 [PMo.sub.6 V.sub.6 O.sub.40 ] in the journal account). An experiment is also reported using this heteropolyacid in 0.87 M sulfuric acid (in the journal account it is cited as 1 M sulfuric acid and the "pH" is stated to be ca.-0.3.). The extra acid is said to be slightly detrimental: up to about 32 turnovers on Pd were obtained in about 120 minutes. The various P-Mo-V co-catalysts are said to be longer lasting in the "pH" range 1-2.
U.S. Pat. Nos. 4,434,082; 4,448,892; 4,507,506; 4,507,507; 4,532,362; and 4,550,212, assigned to Phillips Petroleum Company, disclose systems for oxidizing olefins to carbonyl compounds comprising a palladium component, a heteropolyacid component, and additional components. U.S. Pat. No. 4,434,082 and 4,507,507 both add a surfactant and a diluent of two liquid phases, one of which is an aqueous phase, and one of which is an organic phase, U.S. Pat. No. 4,448,892 and 4,532,362 also both add a surfactant and a fluorocarbon. U.S. Pat. No. 4,507,506 adds cyclic sulfones (e.g. sulfolane). U.S. Pat. No. 4,550,212 adds boric acid and optionally a surfactant. The disclosure of heteropolyacids in each of these patents is the same as in Matveev patents, and the heteropolyacids demonstrated by working examples are prepared by the same method as in Matveev patents, including acidification to "pH" 1.00 with sulfuric acid. PdCl.sub.2 is among the palladium components exemplified. Among the disclosed surfactants are quaternary ammonium salts and alkyl pyridinium salts, including chloride salts. However, cetyltrimethylammonium bromide is the only surfactant demonstrated by working example.
The working examples for olefin oxidation among the above patents predominantly demonstrate the one-stage oxidation of individual n-butenes to 2-butanone in the presence of oxygen. U.S. Pat. No. 4,434,082 and 4,507,507 demonstrate oxidation of 3,3-dimethyl-1-butene. U.S. Pat. No. 4,448,892 and 4,532,362 demonstrate the oxidation of 1-dodecene. U.S. Pat. No. 4,507,506 is concerned with the one-stage oxidation of long-chain alpha-olefins and demonstrates oxidations of 1-decene and 1-dodecene.
U.S. Pat. Nos. 4,720,474 and 4,723,041, assigned to Catalytica Associates, disclose systems for oxidizing olefins to carbonyl products comprising a palladium component, a polyoxoanion component, and additionally a redox active metal component (certain copper, iron, and manganese salts are disclosed) and/or a nitrile ligand. The disclosures emphasize the elimination of chloride from the system; the catalyst systems do not contain chloride ions except sometimes as "only trace amounts" resulting from the presence of chloride in the synthesis of the polyoxoanion "in order to form and (or) crystallize the desired structure". The patents disclose that "pH" or acidity can be adjusted by various proton sources, such as an acid form of a polyoxoanion or certain inorganic acids; sulfuric acid is said to be a preferred acid and is the only acid so described. The "pH" of the liquid phase is said to be preferably maintained between 1 and 3 by the addition of appropriate amounts of H.sub.2 SO.sub.4. The working examples for olefin oxidation all add H.sub.2 SO.sub.4 to the reaction solution, either to obtain 0.1 N concentration or to obtain "pH" 1.5 or 1.6.
U.S. Pat. No. 4,720,474 and 4,723,041 demonstrate by working example the oxidation of various olefins to carbonyl products: predominantly 1-hexene, as well as ethylene, 1- and 2-butenes, 4-methyl-1-pentene, cyclohexene, 1-octene, and 2-octene, all in the presence of oxygen. Example XL gives initial olefin reaction rates using a catalyst solution including Pd(NO.sub.3).sub.2, K.sub.5 H.sub.4 PMo.sub.6 V.sub.6 O.sub.40, and Cu(NO.sub.3).sub.2, with H.sub.2 SO.sub.4 added to "pH" 1.5, at 85.degree. C. and 100 psig total pressure with oxygen in a stirred reactor without baffles. The reported ethylene reaction rate is 8.58.times.10.sup.-7 moles C.sub.2 H.sub.4 /sec ml (0.858 (millimoles/liter)/second). This corresponds to a palladium turnover frequency of 0.17 (millimoles C.sub.2 H.sub.4 /millimole Pd)/second. A slightly lower rate is reported for 1-butene.